The phenomenon of scour, i.e., to clear or remove by a current of fluid, is a well known problem associated with rivers and shorelines in association with bodies of moving water. Scouring and erosion mechanisms are present and associated with any river bed or shoreline which is associated with a moving fluid. Scour is especially important when trying to maintain or stabilize the geologic structure of the river or shoreline.
The scour of sediment from the river bed and river bank beneath a body of moving water is a difficult problem. Scour is enhanced with an increase in the velocity of the fluid and the moveability of the material comprising the river bed, river bank or shoreline. Scour is the progressive removal of the material and the transport of this material from one location in the river bed to another location.
It is well known to retard the scouring or erosion process by using sandbags to refill the holes caused by the removed material or for filling in the river bed or river bank which has been altered by the scouring process. Other techniques have also been employed. Of interest is U.S. Pat. No. 3,333,420 to K. W. Henson for a Method and System for Controlling the Course of a River. The Henson patent uses a plurality of fence-like structures with vertical slats for dissipating river flow. Also U.S. Pat. No. 4,279,532 to Gagliardi, et al. for Material and System for Minimizing Erosion provides a silt fence which can be used to minimize the transport of silt by the flow of water. Still further, U.S. Pat. No. 2,341,515 to G. W. Rehfeld for Jetty Structure for Controlling River and Surface Water provides a jetty structure having vertically planar and vertically horizontal woven wire or rods for preventing water from scouring the bottom surface under the horizontally planar rods or wire. Still further, U.S. Pat. No. 449,185 to D. H. Solomon for A Device for Preventing Banks from Caving provides a plurality of radially oriented screens for mounting along a bank and for orienting to radiate from a specific point in the river.
All of the presently known or used devices and methods for preventing, reducing or repairing scour and erosion in the vicinity of a river bed or shoreline address the effects of the scouring process. The devices and methods, some of which are discussed above, are merely engineering techniques that have been developed to deal with a common and universal problem as applied to a specific situation. None of the discussed devices or methods seeks to address the cause of the scouring or erosion.
Numerous and varied factors can enhance the scouring or erosion phenomenon. Of significant importance is the consistency of the material in which the structure is embedded. A river bed consisting of non-cohesive material is extremely susceptible to erosion and scouring forces. Thus, a river bed beneath a body of moving water that consists substantially of silty material, sand or gravel is highly susceptible to the scouring process. The scouring process is enhanced by the presence of such non-cohesive material, since scouring requires the disengagement, suspension and movement of river bed and bank sediments.
Another critical parameter associated with the scouring process is the velocity of the fluid. There exists a critical current velocity associated with, but not exclusive of, the geometry of the river or shoreline and the material or sediment to be transported. Thus, a critical current velocity required to initiate scour can be expressed as a function of, at least, the following parameters: the geometric shape of the river, the velocity of the fluid, the size of the sediment material to be transported, the density of the sediment material to be transported and the shape of the sediment material to be transported.
Scour and erosion can adversely effect the geometric shape and geological structure of rivers and shorelines. For example, due to extremely heavy rains in one particular season, excessive river flow can cause the geologic, and heretofore natural, flow pattern of the river to be deviated. As the non-cohesive sediment making up the river bed is transported, the geologic structure of the river is changed. As water moves down the river bed, the flow velocities change drastically with the geometric shape of the river bed. For example, as the water approaches a river bend, the higher velocities are measured at the outer, radial portions of the bend. Typically, centrifugal forces as well as inertial forces cause the increased radial velocities.
There is thus a need for a variably permeable jetty system which can be ideally designed for river bed or shoreline having a bank, a bed, and associated with a body of moving water, which, provides for the control of scour and erosion in appropriate areas.
It is, therefore, a feature of the present invention to provide a unique variably permeable jetty system for implementation with a river or shoreline having a bank, a bed, and associated with a body of moving water for strategically controlling the different flow velocities associated with the body of moving water.
It is a more particular feature of the present invention to provide a variably permeable jetty system to manipulate and control the transport mechanisms associated with the movement of material in the vicinity of a river bend or shoreline.
Another feature of the present invention is to provide a variably permeable jetty system for controlling the specific flows that cause scour and erosion.
Yet another feature of the present invention is to prevent the impingement, on the sediment material comprising a river bed and bank, of the higher velocity flow associated with a river bend.
Yet still another feature of the present invention is to provide a variably permeable jetty system that reduces the size of the separation of the fluid flow associated with the jetty system for reducing the down stream wake and turbulence associated with the jetty system.
A further feature of the present invention is to provide a variably permeable jetty system for reducing the magnitude of the resistance associated with the variably permeable jetty system while engaging the enhanced scour forces associated with a river bend or shoreline.
Still further a feature of the present invention is to provide a variably permeable jetty system for controlling the scour of, the transport of and the deposition of sediment material forming a river bed or shoreline.
Additional features and advantages of the invention will be set forth in part in the description which follows, and in part will become apparent from the description, or may be learned by practice of the invention. The features and advantages of the invention may be realized by means of the combinations and steps particularly pointed out in the appended claims.